Diesel fuel lines

boatmike

Well-known member
Joined
30 Jun 2002
Messages
7,044
Location
Solent
Visit site
Yes, in fact it is normal to use compression fittings with olives. Alternatively use face seals with copper washers. PTFE will certainly degrade
 

oldharry

Well-known member
Joined
30 May 2001
Messages
9,958
Location
North from the Nab about 10 miles
Visit site
Diesel fuel lines are not normally fitted with threaded unions to make them fuel tight because - you have guessed it! - the threads do not form a perfect seal, and will leak. Hence the advice to use olives and compression fittings.

What exactly is the fitting that is leaking? Should there not be some sort of compression washer to seal it? PTFE will certainly degrade. If you HAVE to use a threaded fitting, then you need to use a sealant such as Blue Hylomar, but even so it is difficult to get a good seal without risking the sealant either restricting the fuel flow, or bits breaking off and being drawn up the line to cause often major problems elsewhere. If using Hylomar. you must clean all the diesel off the threads with meths first, or it may not adhere or form a proper seal.

But sealed threads in a diesel fuel system is not good practice, and should really be avoided.
 

Avocet

Well-known member
Joined
3 Jun 2001
Messages
29,034
Location
Cumbria
Visit site
Does diesel attack PTFE? I thought it was famous for being inert? (agree by the way, you shouldn't have to rely on sealing threads in this sort of application but was curious about PTFE degrading).
 

corncob

New member
Joined
13 Apr 2005
Messages
28
Visit site
Polytetrafluoroethylene or normally known as teflon, is virtualy inert. will only react with certain metals. PTFE is added to most synthetic engine oils, and won't react with diesel. no i am not a chemist, i just searched on the web. Use swagelock compression fittings.
 

Heckler

Active member
Joined
24 Feb 2003
Messages
15,817
Visit site
nothing,
diesel fuel line fittings are designed to seal with their original components.
so if it has an olive and leaks change the olives, if a compression washer change the washer, if it is an injector pipe there is nothing you can use to seal it if it leaks at the fitting, something is broken, change the injector pipe.
ptfe can be used on fittings to try and get you home in an emergency, it is inert and so any cobblers talked about diesel proof or not is exactly that. hylomar is for gaskets not pipe fittings.
stu
 

Evadne

Active member
Joined
27 Feb 2003
Messages
5,752
Location
Hampshire, UK
Visit site
I was a bit concerned about your question until I read some of the answers. I had several fittings replaced over 2 years ago and one of them seemed to be dripping, barely enough to notice but enough to make the boat smell if the fuel was left on for 24 hours. After dismantling I found the cone didn't fit the cup properly so I wrapped ptfe around the thread of the collar and it hasn't dripped since. Seems like I've no real reason to change it.
 

Spyro

Well-known member
Joined
18 Jan 2003
Messages
7,591
Location
Clyde
Visit site
I'm not sure which kind of fittings would require the thread to be sealed I would have thought most would be the "banjo bolt" fittings which as stated before require compression rings. I also seem to recall being advised against any ptfe tape where fuel lines are concerned as a bit could become detached and end up blocking the injectors.
 

oldharry

Well-known member
Joined
30 May 2001
Messages
9,958
Location
North from the Nab about 10 miles
Visit site
[ QUOTE ]

any cobblers talked about diesel proof or not is exactly that. hylomar is for gaskets not pipe fittings.
stu

[/ QUOTE ]

Well thats one point of view, but if you have had to spend the amount of time I have removing little bits of PTFE tape from an injection system, I know you would not be quite so dismissive. Degrade or break up - the end result is the same - a bad mess you really do NOT want to have to deal with. /forums/images/graemlins/frown.gif

And yes, Hylomar is made for gaskets, but if pipe threads are cleaned up and it is applied carefully, it works a whole lot better than PTFE in a diesel application.

But as I said before, neither of these remedies should be necessary if the system is properly set up in the first place with compression fittings and it is bad practice to go down the route of using any form of sealant in the first place.

The original post asked specifically about making threaded fittings diesel proof. My answer is, dont try; but if you really MUST, use Hylomar on cleaned threads, and not PTFE.
 
Top